Diabetic patients are known to have an impaired immune response to viral antigens and a high incidence of atherosclerosis. This study was initiated to evaluate the association between cytomegalovirus infection and atherosclerosis in patients with diabetes mellitus. Patients with diabetes mellitus type 1 and 2 (> 5 years) with (group A) and without (group B) clinical signs of atherosclerosis were included. Cytomegalovirus cultures were obtained, serum was screened for CMV-antibodies and CMV-IgG and CMV-IgM titers were determined. Cytomegalovirus antibodies were detected more often in diabetic patients with atherosclerosis compared to patients without atherosclerosis (70.7 vs. 45.2%, P = 0.018. In female patients the prevalence of CMV-antibodies was 89.5 vs. 40.0% (P = 0.0037). CMV IgG titers were twice as high in group A compared to group B. Cytomegalovirus was cultured from four urine samples and two throat swabs in group B and in one urine and one throat swab in group A. The prevalence of cytomegalovirus antibodies was higher in diabetic patients with atherosclerosis compared to diabetic patients without atherosclerosis. This difference was most striking in the female population. CMV-IgG titers were twice as high in the atherosclerosis group. These data suggest that cytomegalovirus may play a role in the development of clinical atherosclerosis in patients with diabetes mellitus.